package com.lagou.sqlSession;

import com.lagou.enums.SqlCommandType;
import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
        List<Object> objects = selectList(statementId, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public int insert(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.insert(configuration, mappedStatement, params);
    }

    @Override
    public int update(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public int delete(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.delete(configuration, mappedStatement, params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, (proxy, method, args) -> {
            // 底层还是去执行JDBC代码，但是可以根据情况不同调用selectOne、selectList
            // 准备参数 :
            // 1.statementId 接口全限定名.方法名
            String methodName = method.getName();
            String className = method.getDeclaringClass().getName();

            String statementId = className + "." + methodName;
            // 2. params args

            SqlCommandType sqlCommandType = configuration.getMappedStatementMap().get(statementId).getSqlCommandType();
            switch (sqlCommandType) {
                case SELECT:
                    Type genericReturnType = method.getGenericReturnType();

                    if (genericReturnType instanceof ParameterizedType) {
                        List<Object> objects = selectList(statementId, args);
                        return objects;
                    }

                    return selectOne(statementId, args);
                case INSERT:
                    return insert(statementId, args);
                case UPDATE:
                    return update(statementId, args);
                case DELETE:
                    return delete(statementId, args);
                default:
                    throw new RuntimeException("unknown command type");
            }


        });

        return (T) proxyInstance;
    }
}
